By way of background, reference is made to Applicant's prior U.S. Pat. Nos. 3,618,709, 3,888,420 and 5,205,378, as well as co-pending applications Ser. Nos. 07/269,636 and 07/271,001, filed Jul. 1 and 7, 1994, (now U.S. Pat. Nos. 5,542,498 and 5,524,729), and 08/570,806, filed Dec. 12, 1995, together with the various references cited of record therein, all of which are incorporated herein by reference. Collectively, these various references illustrate and describe a number of different components and systems for use in the above field, including generally known forms of a longitudinally reciprocal piston pin-type positivedisplacement pump of the general type toward which the preferred embodiment of this invention, as described more fully below, is directed by way of example. Somewhat more particularly, reference is made to the aforementioned U.S. Pat. Nos. 3,888,420 and 5,205,378, as well as earlier U.S. Pat. No. 3,421,600, and to co-pending application Ser. No. 08,570,806, whose disclosures address or refer to pumps of this type which are commercially available as of the present date.
The reciprocal piston-type positive-displacement pumps noted above incorporate cylindrical pin-like piston members which are moved back and forth through a closely-fitting chamber into which the liquid to be metered out by the pump is conveyed, usually through a lateral passage which opens into the metering chamber. Typically, the chamber fills during the return stroke of the piston, and the charge of liquid which has entered the chamber is then forced out by the forward stroke of the pin or piston. In this manner, precise volumetric charges of liquid are repeatedly ejected from the pump, with the particular volume of the ejected liquid charges corresponding directly to the effective volume of the metering chamber. Accordingly, the size of the metered volumes may be changed by changing the effective size of the metering chamber, and one known way of doing this (apart from simply resizing the chamber and piston) is to vary the length of the piston stroke. This may be accomplished in various ways, such as by changing an actuating cam, electrical solenoid, or compressed air charge used to reciprocate the piston (which is usually spring-loaded for its return stroke); however, another and simpler way of doing this is to incorporate some sort of mechanical adjustment feature, such as by threading the piston pin itself, on the portion thereof external to the metering chamber and valve body containing the latter, and then threading a nut or other such member onto the threaded portion of the piston pin, and using the nut as a stop member by letting it contact some fixed referenced point (an example of this being shown in the aforementioned co-pending application Ser. No. 08/570,806).
Various difficulties, in conveniences or limitations are typically presented by such prior art apparatus. For example, those involving cam changes and the like are difficult and time consuming to implement, and are limited in the degree of variability from one configuration to the next. Other types of mechanisms are less complicated but often imprecise and difficult or inconvenient to use. The use of threaded piston rods and the like, as noted above, has the virtue of simplicity and continuous variability, but it may well involve difficult or limited access, inadvertent and undesired changes in the position of parts thought to have been placed where desired, and the lack of any meaningful indicia relating one position of adjustment with another.